The widespread adoption of emerging technologies such as flat panel displays (FPD) and solar cells depends on the ability to manufacture electrical devices on low cost substrates. In manufacturing FPD, pixels of a typical low cost flat panel display (FPD), are switched by thin film transistors (TFT) which may be typically manufactured on thin (−50 nm thick) films of amorphous silicon deposited on inert, glass substrates. However, improved FPDs demand better performing pixel TFTs, and it may be advantageous to manufacture high performance control electronics directly onto the panel. One advantage may be to eliminate the need for costly and potentially unreliable connections between the panel and external control circuitry.
Current FPDs contain a layer of Si that is deposited onto the glass panel of the display via a low temperature deposition process such as sputtering, evaporation, plasma enhanced chemical vapor deposition (PECVD), or low pressure chemical vapor deposition (LPCVD) process. Such low temperature processes are desirable, as the panel used to manufacture FPD tends to be amorphous and has glass transition temperature of approximately 600° C. If manufactured above 600° C., the panel may have a non-uniform or uneven structure or surface. Higher temperature tolerant glass panels such as quartz or sapphire panel exist; however, the high cost of such glasses discourages their use. Further cost reduction would be possible if cheaper, lower temperature tolerant glass or plastic panels could be used.
The low temperature deposition process, however, does not yield optimal Si film. As known in the art, solid Si has three common phases: amorphous, poly-crystalline, and mono-crystalline phases. If Si is deposited at low temperature, the deposited Si film tends to be in an amorphous phase. The channels of thin film transistors based on amorphous Si film may have lower mobility compared to those on either poly-crystalline Si or mono-crystalline Si films.
To obtain a polycrystalline or mono-crystalline Si layer, the panel may undergo further processes to convert the amorphous Si film to either polycrystalline or mono-crystalline film. To obtain a panel with poly-crystalline Si film, the panel may undergo an excimer laser annealing (ELA) process. An example of the ELA process may be found in more detail in U.S. Pat. No. 5,766,989. To obtain a panel with larger crystals, the panel may undergo a process known as Sequential Lateral Solidification (“SLS”) process. An example of SLS process may be found in U.S. Pat. No. 6,322,625. Although ELA and SLS processes may result in a panel with mono-crystalline or poly-crystalline Si thin film, each process is not without disadvantages. For example, excimer lasers used in both processes may be expensive to operate, resulting in an expensive TFT. In addition, the duty cycle may not be optimum for the best conversion of amorphous Si into crystalline Si. Further, the excimer laser may have pulse-to-pulse variations and spatial non-uniformity in the delivered power which may affect the uniformity of the processes. There may also be intra-pulse non-uniformity which may be caused by for example, self-interference of the beam. Such inter-pulse and intra-pulse non-uniformity may result in Si films with non-uniform crystals.
As such, new methods and apparatus for particle processing for the cost effective and production worthy manufacture of high quality crystalline materials on low temperature substrates are needed.